Conventionally, materials such as copper, graphite, which is a carbon material, tungsten-copper, tungsten-silver, and graphite-copper are used as electrode materials for electrical discharge machining. Among them, tungsten-copper, tungsten-silver, and graphite-copper materials are particularly suitable for use in electric discharge machining of difficult-to-machine materials with a high-melting point, such as cemented carbide.
Each of these materials has the characteristics as a material suitable for electrical discharge machining. However, copper has a low melting point, so it is not suitable for use in electrical discharge machining of a cemented carbide material, which has a high-melting point. The tungsten-copper and tungsten-silver materials themselves have a high-melting point, so they are capable of electrical discharge machining of cemented carbide material, which has a high-melting point and is a difficult-to-machine material, or the like, with low electrode wear. However, these materials have poor machine processability into an electrode shape, and another drawback of these materials is that the material cost and the manufacturing cost are significantly higher than those of graphite-based materials. Graphite alone and a graphite-copper material are less expensive than tungsten-copper and tungsten-silver materials, and they are also excellent in machine processability. A problem with these materials, however, is high electrode wear.
For the purpose of improving machine processability of the tungsten-copper electrode, a method of producing a discharge electrode by infiltrating copper into tungsten powder using a metal infiltration method is disclosed (Patent Literature 1). With the just-mentioned manufacturing method, however, it is difficult to change the ratio of tungsten and copper because of the constraint on the manufacturing method. Therefore, it cannot solve the above-mentioned problem with the material made of tungsten-copper.
On the other hand, a method of manufacturing a copper-tungsten alloy by sintering is disclosed (Patent Literature 2). The just-mentioned manufacturing method, however, has the following problems. It is difficult to obtain a material with a uniform composition in the case that the electrode size is large. Moreover, addition of an additive for improving formability may rather degrade the discharge characteristics.
On the other hand, it is believed that the reason for high electrode wear with the graphite-copper material is that when the graphite-copper material is used as the electrode, heat is likely to accumulate and arc tends to occur easily. In order to improve the problem, a method of melt-infiltrating aluminum containing silicon into a graphite material is disclosed (Patent Literature 3).